A fiber reinforced plastic constituted with a reinforcing fiber and a matrix resin has drawn attention in industrial applications since it is high in specific strength and specific modulus, excellent in mechanical characteristics, and has high performance characteristics such as weather resistance and chemical resistance, and its needs are increasing year by year.
To efficiently exhibit lightness which is one of the big characteristics of fiber reinforced plastic molded article, it has been done to form a protrusion portion called as rib on a surface of molded article. By this way, it is possible to increase rigidity and strength of the molded article without increasing thickness of the molded article.
To prevent a curl or the like of a broad flat portion of the molded article, a presence of the rib is effective. Other than the rib, in a structure constituted with plural members, a fitting called as boss used in concave portion or a protrusion portion for adjusting positions at connecting molded articles with each other are widely used.
As molding method of a fiber reinforced plastic, in particular, of a fiber reinforced plastic having high performance characteristics, it is most general to employ an autoclave molding in which semi-cured state products called as prepreg, in which reinforcing fibers are impregnated with a matrix resin, are laid up, and the matrix resin is cured by beating and pressing in a high temperature high pressure oven (autoclave), to be molded into a fiber reinforced plastic. As a molding method which is more excellent in productivity compared to the autoclave molding, RTM (resin transfer molding) molding, in which a fiber base material is shaped into a desired shape, and then impregnated with a resin, is also employed.
As configuration of the reinforcing fibers used in these molding methods, it is general to use continuous fibers in which high mechanical characteristics are easy to be achieved.
As means for forming a protrusion portion such as rib or boss to the fiber reinforced plastic molded article constituted with the continuous fibers, method of bonding a protrusion portion molded beforehand by autoclave molding or the like to a plate portion which is also molded beforehand, with an adhesive or the like, or insert injection molding in which a protrusion portion is molded to a plate portion molded beforehand by autoclave molding or the like, are mentioned.
However, in case of the former, it necessitates a very troublesome process in which a plate portion and a protrusion portion are prepared respectively, and further, they are bonded, and furthermore, there was a problem that an adhesion of the bonded portion must be considered. In case of the latter, since physical characteristics of the protrusion portion mostly formed by injection molding are low, its effect is small especially as a rib, in addition, adhesion properties between the plate portion and the protrusion portion are not good in some cases, and there was a problem that it is easy to be peeled off at the bonded portion.
As other means, a method in which a fiber base material is shaped into a shape of protrusion portion beforehand, and molded by an RTM molding or the like is mentioned, but there were problems that, since a lot of work and time is necessary for shaping the fiber base material, it cannot be said to be good in productivity, although it is better in productivity compared to autoclave molding, and only a protrusion portion of a simple shape can be molded, etc.
On the other hand, in case of a short fiber reinforced plastic of which reinforcing fiber length is about several to several ten mm, it is relatively easy to form a protrusion portion. For example, it is possible to employ, when the matrix resin is a thermosetting resin, press molding or the like such as by SMC (sheet molding compound) or BMC (bulk molding compound), and in case of a thermoplastic resin, injection molding or the like.
However, in the SMC or BMC, in its production process, since a distribution unevenness or an orientation unevenness of reinforcing fibers is unavoidable, there were problems that mechanical characteristics of molded article decreases or, its physical characteristic values vary widely. On the other hand, in the injection molding, since it is possible to mold only when a content of the reinforcing fibers is small and each of which length is short is used, mechanical characteristics of the molded article become very low. Accordingly, in these methods, there was a problem that it is difficult to produce a fiber reinforced plastic having a protrusion portion suitable for a structural member.
An attempt to solve problems of these prior arts is proposed (JP-S63-087206 A). In JP-S63-087206 A, a production method of molded article provided with a rib based on a press molding is disclosed. In the production method, by cutting fibers at the rib portion, the cut fiber ends are poured into the rib end to fill the fibers in the rib.
However, in the case where fibers are cut only at the rib portion, since fibers are not cut at other portion than the rib, fibers are bound as a whole and it is an actual circumstance that the fibers are difficult to be filled up to the rib end. Even when a molded article filled with the fibers up to the rib end could be made by this production method, although the rigidity in direction in which the rib is formed (in direction of rib height) is improved, the rigidity in rib thickness direction depends on, since the fibers are cut, the rigidity only of resin, and therefore the rigidity becomes very low, and the molded article cannot be used as an actual structural member in some cases.
As stated above, a fiber reinforced plastic having a protrusion portion capable of being molded easily, and in addition, excellent in mechanical characteristics has not been found, so far.
It could therefore be helpful to provide a fiber reinforced plastic, having a protrusion portion excellent in mechanical characteristics, in which the problems of prior arts are improved, and a production method thereof.